FIG. 28 is a diagram showing a schematic cross-sectional configuration of a conventional resin-mold package type semiconductor device.
An IC chip 20 is mounted on a specific face 11 of a heat sink 10, sandwiching an adhesive 30, which is made of a resin to serve as a conductive adhesive, in conjunction with the specific face 11. The IC chip 20 is electrically connected to each of leads of a lead frame 40 by a wire 50. The heat sink 10, the IC chip 20, and the lead frame 40 are sealed in a mold resin package 60, which encloses the heat sink 10, the IC chip 20, and the lead frame 40.
The heat sink 10 has the specific face 11 mentioned above, another face 12 and a side face 13 between the specific face 11 and the other face 12. The side face 13 has a protrusion (a coining) 14. By letting the protrusion 14 bite into the mold resin package 60, the strength of adhesion existing between the mold resin package 60 and the heat sink 10 can be increased.
In the semiconductor device of such a resin-mold package type, the heat sink 10 made of a material such as Cu to excellently avoid dissipation of heat in the semiconductor device is embedded.
However, in the semiconductor device of such a resin-mold package type, thermal stress due to cooling-heating cycles, a solder re-flow generated at a solder-mounting time or the like causes the heat sink 10 and the mold resin package 60 or the heat sink 10 and the resin adhesive 30 to be detached from each other with ease. This is because there is a big difference in thermal expansion coefficient between the heat sink 10 made of a metal or the like and the resins, i.e., the mold resin package 60 and the resin adhesive 30.
Then, the occurrence of such detachment raises a performance-deterioration problem caused by, among others, the fact that a crack is resulted in at a relatively early time in the mold resin package 60 due to a thermal shock and the fact that thermal and electrical resistances between the IC chip 20 and the heat sink 10 increase.
In addition, a soldering material free of Pb (Plumbum) is desirable but the fusion temperature of such a soldering material is high. Thus, when the semiconductor device described above is joined to an external substrate through a soldering material, the temperature of a solder re-flow increases from 225 degrees Celsius of the conventional soldering material containing Pb to a higher temperature in the range 240 to 260 degrees Celsius. As a result, the problem described above becomes even more serious.